The invention lies in the telecommunications field. More specifically, the invention relates to a method and a radio communications system for transmitting data in a GSM mobile radio network, in particular between base stations and mobile stations, over a TD/CDMA radio interface.
The mobile radio network has at least one base station controller (BSC) and a first base station (BS) assigned to a radio cell. At least one first frequency channel is made available between the first base station (BS) and the mobile stations (MS) in order to transmit data and to transmit signaling information with a TDMA transmission method according to the GSM standard. The first base station (BS) additionally makes available a second broadband frequency channel with a TD/CDMA transmission method, according to a standard of the third generation of mobile radios, and a connection (V1) is set up in the first or second frequency channel. A first base station (BS) of the system contains at least one transmitter/receiver device for a second broadband frequency channel with a TD/CDMA transmission method, and the base station controller is embodied in such a way that a connection setup for a connection is controlled in the first or second frequency channel. Such a method and radio communications system are described by Jurgen Mayer et al., in xe2x80x9cProtocol and Signaling Aspects of Joint Detection CDMA,xe2x80x9d Proceedings of 8th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications-PIMRC ""97, Vol. 3, Sep. 1, 1997, pages 867-71, Helsinki, Finland.
U.S. Pat. No. 5,600,707 (European published patent application EP 0 700 225) describes a radio system which has a base station with a TDMA transmission unit and a wireless ISDN transmission unit. A TDMA channel with a low data rate is used to set up a wireless ISDN connection provided with a high data rate.
U.S. Pat. No. 5,793,757 (International PCT publication Wo 97/30526) describes a mobile radio system with so-called dual mode base stations which support both timeslots with FDMA/TDMA channels and timeslots with CDMA channels.
In mobile radio networks, messages (for example voice, image information or other data), are transmitted using electromagnetic waves over a radio interface between a transmitting radio station and a receiving radio station (base station or mobile station). The electromagnetic waves are irradiated here with carrier frequencies which lie in the frequency band provided for the respective system. In the case of the GSM (Global System for Mobile Communication), the carrier frequencies lie in the region of 900, 1800 or 1900 MHz. For future mobile radio networks using TDMA or TD/CDMA methods for transmitting over the radio interface, for example the UMTS (Universal Mobile Telecommunications System) or other 3rd generation systems, frequencies in the frequency band of approximately 2000 MHz are provided.
German published patent application DE 195 49 148 discloses a radio communications system which utilizes CDMA subscriber separation (CDMA Code Division Multiple Access), the radio interface additionally having time-division multiplex subscriber separation (TDMA Time Division Multiple Access). Consequently, a TD/CDMA transmission method is used for the radio interface. At the receive end, a JD (Joint Detection) method is used to perform improved detection of the transmitted data based on the knowledge of spread codes of a plurality of subscribers. Here, it is known that at least two data channels can be assigned to a connection over the radio interface, it being possible to distinguish each data channel by means of an individual spread code. The radio communications system which is used in this context is a candidate for a system of the 3rd generation of mobile radios.
The article by P. Vary, xe2x80x9cImplementation Aspects of the Pan-European digital mobile radio systemxe2x80x9d IEEE 1989, pp. 4-17 to 4-22, discloses the structure of a GSM radio station with RF component, filters, channel estimators, modulators/demodulators, channel encoders/channel decoders. The GSM standard uses a combination of FDMA (Frequency Division Multiple Access) and TDMA for the radio interface and has met with acceptance throughout the world. This standard is used to provide services to over 20 million subscribers in Europe alone. There has already been extensive investment in the infrastructure and in mobile stations.
The transition from the 2nd generation of mobile radios (GSM) to the 3rd generation of mobile radios will again require considerable investment on the part of the network operators if network elements such as mobile switching center, mobile station controller or base stations have to be replaced or installed additionally. Significant development costs will also be incurred by the manufacturers of the infrastructure and mobile stations.
It is accordingly an object of the invention to provide methods and radio communications systems for transmitting data in a mobile radio network, which overcome the disadvantages of the heretofore-known devices and methods of this general type and which make it possible to migrate from an existing GSM mobile radio network favorably in terms of cost and effort.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of transmitting data in a mobile radio network having a first base station assigned to a radio cell, which comprises the following steps:
making available, with a first base station assigned to a radio cell, a first frequency channel for data transmission and an organization channel for transmitting signaling information with a transmission method according to a first mobile radio standard;
additionally making available, with the first base station, a second frequency channel with a transmission method according to a second mobile radio standard; and
signaling via the organization channel of the first mobile radio standard the standards supported in the radio cell.
In accordance with an additional feature of the invention, a connection is set up in the first or in the second frequency channel; and the connection is handed over to the respectively other frequency channel without selecting a second base station.
In accordance with another feature of the invention, the first mobile radio standard is a GSM standard and the second mobile radio standard is a third generation mobile radio standard.
The system is preferably implemented in the popular GSM mobile radio network having at least one base station controller and one first base station. At least one first frequency channel is made available between the first base station and mobile stations in order to transmit data and to transmit signaling information. In a specific embodiment, the first base station additionally makes available a second broadband frequency channel with a TD/CDMA transmission method. After a connection has been set up in the first or second frequency channel, a handover of the connection to the respective other frequency channel is carried out by the base station controller without a second base station being selected.
This means that, a new transmission method is provided on the basis of an already existing base station system by retrofitting a base station which is already installed in the GSM network, this fact applying equally to the carrier frequencies in the 900, 1800 and 1900 MHz ranges. Thus, no additional expenditure or effort is needed to provide a new base station system. By incrementally retrofitting the base stations, the coverage is improved in a way which permits the additional radio capacity to be provided where there is an adequate level of demand for it. This thus reduces the investment risks for network operators.
Without neglecting the provision of services to GSM mobile stations, it is possible to ensure, on a selective basis, that coverage is provided to mobile stations which use the radio interface according to a TD/CDMA transmission method. For mixed mode mobile stations which can use both frequency channels, complete coverage is ensured and additional, new, higher-rate services can be provided in specific regions.
The handover of the connection does not only include connections which have already been set up but can also be applied in cases in which the mobile station receives organizational or signaling information, or transmits signaling information, in one frequency channel, advantageously the first frequency channel, but the useful information is transmitted in another frequency band, for example the second frequency band.
The migration from existing GSM mobile radio networks to a 3rd generation radio communications system is thus significantly simplified. The TD/CDMA transmission method combines advantages of the known TDMA transmission method with those of the simple implementation of higher-rate services with a variable data rate using a CDMA subscriber separation method, both transmission methods using the same timing pattern.
The broadband configuration of the second frequency channel enables the transmitter/receiver devices to be manufactured more economically in comparison with a large number of narrow band frequency channels because fewer RF components are required and better and cheaper digital signaling processing means are progressively making the processing of signals easier at the receive end and the transmit end.
According to one advantageous development of the invention, the frequency bands of the first and second frequency channels overlap. This means that the TD/CDMA transmission method is used in frequency bands which have been kept available in the GSM mobile radio system. By means of appropriate frequency planning, the plurality of coherent frequency bands are assigned at least to individual base stations, and the frequency bands are then also used by the second, broader band frequency channel. This is implemented in a particularly advantageously way if the frequency band of the second frequency channel comprises at least eight frequency channels with a bandwidth equal to the first frequency channel. The second frequency channel has, for example, a bandwidth of 1.6 or 3.2 MHz and thus comprises eight or 16 previous 200 kHz narrowband GSM frequency bands. The second frequency channel is therefore adapted to the frequency and timing pattern of the GSM mobile radio network.
A further advantageous embodiment of the invention provides for the first and second frequency channels to be implemented in the same frequency band but in different timeslots. This is advantageous particularly in radio cells in which coverage is to be provided for GSM, TD/CDMA, and mixed mode mobile stations without requiring additional frequency bands. The timeslots can be distributed between the two transmission methods according to demand.
The distribution of a plurality of connections among the timeslots is advantageously controlled by the base station controller in such a way that a timeslot of a TDMA or TD/CDMA transmission method is handed over for the respective other transmission method. This means that the timeslots are filled with connections to a satisfactory degree and, when there are fluctuations in demand, as many timeslots as possible are assigned to a transmission method for which there is greater demand. In this way, none of the individual GSM timeslots block the use of a timeslot over the entire bandwidth of the second frequency channel which has a higher transmission capacity. The same applies to redistribution of the connections in the opposite direction.
The handover of a connection to the respective other transmission method is carried out as soon as the capacity utilization of the frequency channel drops below a first threshold value or the ratio of mobile stations with TD/CDMA compatibility to other mobile stations within a radio environment reaches a second threshold value. By introducing the threshold values, the previous demand or the future demand which can be derived from the mobile stations located in the radio cell is estimated and the radio resources are used in the best possible way by distributing the connections at the appropriate time.
With the above and other objects in view there is also provided a novel radio communications system, comprising:
a base station assigned to a radio cell of the radio communications system, the base station being designed to transmit data in a first mobile radio standard in a first frequency channel;
the base station having at least one transmitter/receiver device (TRX2, TRX3) for a second frequency channel with a transmission method according to a second mobile radio standard; and
the base station signaling via an organization channel for transmitting signaling information with a transmission method according to the first mobile radio standard the standards supported in the radio cell.
In other words, the radio communications system has a plurality of base stations, the first of which supports both frequency channels and the second only supports the TDMA transmission method of the GSM standard, handovers of connections from the second base station without TD/CDMA compatibility advantageously take place preferably to the first base station. By virtue of the two frequency channels, the second base station will have more extensive radio resources. The handovers between the base stations can also be performed according to the principles and threshold values mentioned above.
In each base station the GSM mobile radio network provides organizational and signaling channels which are available over large areas. The signaling information of the first frequency channel is advantageously used for handing over connections or for a connection setup. In this way, even in the case of frequency channels which do not overlap, no additional signaling complexity, or only a slight degree of signaling complexity, becomes necessary and additional capacity can be put to better use for a transmission of useful information.
A further advantageous development of the invention provides for an interrogation of a desired data rate to be carried out for handing over connections or for a connection setup, and for the first or second frequency channel to be selected after this. In this way, an appropriate allocation of a transmission method can be prepared even during a connection setup or when a higher or lower data rate is desired during the connection. In this context, the first frequency channel is more suitable for transmitting voice and lower data rates, and the second frequency channel is more suitable for higher-rate services (Internet or Multimedia Services).
The retrofitting of the base station is carried out using additional transmitter/receiver devices for the TD/CDMA transmission or by replacing a GSM transmitter/receiver device by a common transmitter/receiver device for both transmission methods. Despite the retrofitting, it is, however, possible to use common modules, for example antennas, RF components, amplifiers, synchronization and clock modules, interfaces to the base station controller etc., commonly.
The scope of the invention includes the fact that the first and second frequency channels are assigned to different cell sizes in accordance with a hierarchical cell model. During a migration phase, it may be advantageous to provide the second frequency channel for the TD/CDMA transmission only in specific highly restricted areas (xe2x80x9chot spotsxe2x80x9d), i.e. thus to specify microcells or to equip macrocells for radio cells with generally lower densities on new mixed mode mobile stations.
The method according to the invention also provides freedom of maneuver in the ratio of uplink direction and downlink direction. For the purpose of asymmetrical transmission of information, as is required for multimedia services, it is possible to use different data rates in the two transmission directions. Alternatively, identical frequency bands, but different timeslots, can be used in the uplink and downlink directions. In this way, the use of DECT radio communications systems can also be included.
As an alternative to TD/CDMA methods, it is possible, as is described in the above-mentioned German patent publication DE 195 49 148 (incorporated by reference), for the second frequency channel to use other methods which are based on the same time frame structure as the GSM mobile radio network but use spreading according to a frequency jump sequence or a broadband transmission according to OFDM transmission as in European patent publication EP 97 105 149 (incorporated by reference).
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and radio communications system for transmitting data, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.